There are many criteria that require fastener characteristics that cannot be easily obtained with metallic fasteners. For example, electrical insulation, sealing out moisture, corrosion resistance, heat transfer resistance, or combinations thereof fall into this category.
It is possible to make bolts, nuts, and other hardware all of a synthetic material, or, as is done in some cases a combination, for instance, a metallic bolt with a synthetic head or nut to meet specific requirements. One limitation has been to provide a bolt head or nut that will allow sufficient torque to be applied with standard wrenches that might be encountered in day to day operation.
Wrenches for a given size hex bolt or nut are usually available in either six or twelve points. The difference between these two configurations can cause some problems when they are used on standard metallic heads. However, the difference becomes quite significant when synthetic materials form the hexagonal head or nut.
Naturally the nut and bolt art is quite highly developed as well as the wrench art where six and twelve sided nuts are handled with various types of socket wrenches.
Examples of patents which are directed to materials and head structure include Swiss Pat. No. 294,797 and U.S. Pat. Nos. 3,731,961; D-157,484; D-187,818; D-203,947; D-220,027; and D-233,735.
Examples of types of wrenches which have been designed to handle six and twelve sided nuts are recognizable in U.S. Pat. Nos. 1,106,752; 2,106,749; 2,337,368; 2,502,587; 2,651,230; 2,991,678; 3,433,108; 3,835,737; and French Pat. No. 1,263,619.
It has been found that use of a six point wrench on a hexagonal head of synthetic material will allow sufficient torque to be applied on heads that are molded onto a metallic shank or bolt. It is also possible to utilize the elastic limit of the material as a safety factor to prevent too much force being applied and causing the head to rotate in relation to the shank. When the elastic limit is reached, the corners of the hexagonal head will bend, allowing the wrench to slip. It the material has been properly chosen, it will return to its original shape when the pressure is removed insuring that it is suitable for removal with the same wrench and re-use.
If a twelve point wrench is used on this same hexagonal head, the presence on the corners of the synthetic material is on a smaller area which generally results in either or both of the following. First, the corners will cam before sufficient torque can be applied to accomplish the desired function. Second, the increased pressure per unit area causes the synthetic material to flow so that the head is not re-usable.
One possible solution to this situation is to fabricate a twelve point head, or bolt, for use with a twelve point wrench. Of course it is not possible to utilize a six point wrench on this twelve point head.
Accordingly, there is clearly a need for a more versatile head particularly when dealing with synthetic type fastener elements which can be easily and effectively handled with different types of tools at hand such as six and twelve point wrenches.